The invention is related to the field of data storage systems.
Data storage systems are known that provide so-called “storage as a service” operation in which storage capacity is given to users on a contract basis (e.g., a subscription). The service may be provided over a public network such as the Internet. In this model, users are presented with storage in the form of “virtual disks” that from the users' perspective have all the attributes of real physical storage devices, including for example respective total storage capacities and perhaps certain quality-of-service or QOS parameters. Each virtual disk is mapped to a region of a physical storage device where the underlying real physical storage is provided.
In storage systems including those providing storage as a service, it is known to use a technique called “overprovisioning” so that the sum of the storage capacities of a set of virtual disks that are assigned to a given storage device exceeds the storage capacity of the storage device. This technique exploits the knowledge that most or all users are not always using all the storage capacity of their respective virtual disks. With some knowledge or assumptions about actual usage patterns, a system operator assigns virtual disks to storage devices so that there is sufficient real physical storage capacity for expected actual usage.